Traditional designs of internal combustion engines permit for unwanted air pollution and loss of fuel due to evaporation of fuel, containing hydrocarbon (HC), from the tank, the carburetor, and other engine component. There are known prior art to obviate these problems.
In particular, there is an evaporative fuel control system which employs a fuel vapor collection canister containing an adsorbent material, such as activated carbon, for adsorbing evaporative fuel, and a purge system for releasing the adsorbed fuel and supplying it to the engine during operation of the engine. See JP Laid-Open No. 2004-11561 and JP Laid-Open No. 2004-28060.
As shown in FIG. 3, the evaporative fuel control system 202 is associated with a conventional internal combustion engine.
This evaporative fuel control system 202 includes a canister 212, an atmosphere open passage 214, and a purge valve 216. The canister 212 is disposed on an evaporative fuel control passage 210 connecting a fuel tank 208 with an intake passage 206 in an intake pipe 204 of the engine (not shown) mounted on a vehicle (not shown). The atmosphere open passage 214 connects the canister 212 with the atmospheric air. The purge valve 216 is disposed between the intake passage 206 and the canister 212.
As shown in FIG. 3, the evaporative fuel control passage 210 connects the fuel tank 208 with the intake passage 206 on the downstream side of a throttle valve 218. A controller 224 is connected to the purge valve 216, a fuel level gauge 220 within the fuel tank 208, and a leak check module 222 associated with the atmosphere open passage 214.
As also shown in FIG. 3, the leak check module 222 is located on the atmosphere open passage 214 between the canister 212 and an air filter 226. This leak check module 222 includes first, second and third atmosphere open passages 214-1, 214-2, and 214-3. More particularly, the first atmosphere open passage 214-1 connects the canister 212 and the air filter 226 through a solenoid switching valve 228. The second atmosphere open passage 214-2 connects the canister 212 and the air filter 226 through the solenoid switching valve 228 and a pressure reducing pump 230. The third atmosphere open passage 214-3 connects the canister 212 and the air filter 226 through a reference orifice 232 and the pressure reducing pump 230. A pressure sensor 234 is disposed between the reference orifice 232 of the third atmosphere open passage 214-3 and the pressure reducing pump 230.
Further, the evaporative fuel control system 202 permits the canister 212 to absorb the evaporative fuel generated in the fuel tank 208, and supplies the evaporative fuel absorbed in the canister 212 to the intake passage 206 through the purge valve 216 for a purge control.
One method to examine leakage in the evaporative fuel control system 202 employs the pressure reducing pump 230 or the electric pump, the solenoid switching valve 228, and the reference orifice 232.
In this method, as shown in FIGS. 4 and 5, after activation of a leakage diagnosis system, the pressure reducing pump 230 or the electric pump is activated to vacuum or generate a negative pressure (pressure less than an ambient atmosphere), thereby causing the atmosphere through the reference orifice 232, and a reference pressure is measured.
Then as shown in FIGS. 4 and 6, the switching valve 228 is activated to vacuum the fuel tank, and a pressure is measured after elapse of predetermined time D. Thereby, it is determined whether there is leakage (large leakage which is greater than the reference pressure generated by the flow of atmosphere through the orifice) by comparing the pressure measured after predetermined time D with the reference pressure.
However, there is a possibility that the above-mentioned leakage diagnosis method determines that the evaporative system is in a normal condition without leakage, even if one of the components, the switching valve, is in failure.
There is a method to diagnosis the closed switching valve (JP Laid-Open No. 2003-13810). This method cannot, however, diagnosis the failure of the opened switching valve.
Incidentally, FIG. 3 shows an example of the existing leakage diagnosis system. Shown is the illustrated leakage check module 222 integrating thereinto the pressure reducing pump 230, the orifice 232, and the pressure sensor 234, although these components may not be integrated. Also, the leak check module 222 is attached to an atmosphere side of the canister 212. During the reduction of pressure in the evaporative system for the leakage diagnosis, the switching valve 228 is activated (placed in a shutoff state). Otherwise, the switching valve is deactivated (placed in an open state), thereby connecting the evaporative system 202 to the atmospheric air.
Referring to FIG. 4 which illustrates control by the existing system, after the leak diagnosis begins when a certain diagnosis condition is satisfied, and after the pressure reducing pump is actuated, the switching valve 228 is switched from an opened state (deactivated) to closed state (activated) and the whole system is vacuumed by the pressure reducing pump 230 which pumps atmosphere out of the system, thereby generating a negative pressure within the system. It is determined that there is a leakage below a reference value if the pressure being reduced is below a pressure P2, and that there is a leakage above the reference value if the pressure is not reduced below the pressure P2 after a certain elapsed time. Then, the pressure reducing pump 230 is deactivated and the switching valve 228 is opened (deactivated), and the leak diagnosis ends.
Further, FIG. 5 shows airflow while the switching valve 228 is deactivated and the pressure reducing pump 230 is activated. Also, FIG. 6 shows airflow while the switching valve 228 is activated and the pressure reducing pump 230 is deactivated.
FIGS. 8 and 9 illustrate transition of pressure when the switching valve 228 of the existing system is in failure and remains or becomes fixed in an opened or closed state. In both cases, there is a high possibility that a normal condition is determined when a leakage determination pressure variation ÄP3 (ÄP3=P4−P2) is less than LEAK (wherein LEAK is a certain value set around 0 [kPa]).
Now the operation of the control for the existing system is explained with reference to FIG. 7.
After a program for the control starts in step 302, a determination is made in step 304 as to whether a monitoring condition is satisfied. If the determination in step 304 is “NO”, the program ends in step 306. If the determination in step 304 is “YES”, then a process for measuring an initial pressure P1 is performed in step 308.
Then performed are a process for activation of the pressure reducing pump in step 310, a process for measuring pressure P2 after a certain time T1 has elapsed in step 312, and a process for calculation of a reference pressure variation ÄP1 (ÄP1=P1−P2) in step 314. Then a determination is made in step 316 whether the reference pressure variation ÄP1 is less than a first reference value for the reference pressure DP11 (ÄP1<DP11).
If the determination in step 316 is “NO”, then another determination is made in step 318 whether the reference pressure variation ÄP1 is greater than a second reference value for the reference pressure DP12 (ÄP1>DP12). If the determination in step 316 is “YES”, then it is decided in step 320 that the reference pressure variation ÄP1 is extremely low. Then a process to deactivate the pressure reducing pump is performed in step 322, and the program returns in step 324.
If the determination in step 318 is “NO”, then a process for activating (closing) the switching valve is performed in step 326. If the determination in step 318 is “YES”, then it is decided in step 328 that the reference pressure variation ÄP1 is extremely high. Then the process to deactivate the pressure reducing pump is performed in step 322, and the program returns in step 324.
After the process for activating (closing) the switching valve in step 326, a process to measure a maximum pressure P3 over a predetermined time T2 is performed in step 330. Then performed are a process to calculate a valve switching pressure variation ÄP2 (pressure variation when the switching valve is shifted or switched; ÄP2=P3−P2) in step 332, a process to update a pressure P4 being reduced in step 334, and a process to calculate a leak determination pressure variation ÄP3 (pressure variation for leak diagnosis; ÄP3=P4-P2) in step 336. A determination is made in step 338 whether a certain time T3 has elapsed since activation (close) of the switching valve.
If the determination in step 338 is “NO”, then a determination is made in step 340 whether the leak determination pressure variation ÄP3 is below a leak value LEAK (ÄP3<LEAK). If the determination in step 338 is “YES”, a process to decide “failure for leakage” is performed in step 342.
Further, if the determination in step 340 is “NO”, the program returns to the process for updating the reducing pressure P4 in step 334. If the determination in step 340 is “YES”, a process to decide a “normal condition” is performed in step 344.
After the process to decide the “failure for leakage” in step 342 or the process to decide the “normal condition” in step 344, a process to deactivate the pressure reducing pump and deactivate (open) the switching valve is performed in step 346, and the program returns in step 348.